Method of producing chromium plated tools



Patented Dec. 29, 1931 UNITED STATES PATENT OFFICE BYRON V. MCBRIDE, OF IRWIN, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELEG- TRIC MANUFACTURING COMPANY, A ('1OIRIORA'JPIONv OF PENNSYLVANIA METHOD OF PRODUCING CHBOMIUH PLATED TOOLS No Drawing.

My invention relates to tools and implements of all descriptions having one or more cuting edges or pressing surfaces and more particularly to a process of coating the cutting edges or pressing surfaces of such tools or implements with a protective layer of chromium.

An object of my invention is to provide the surfaces of cutting or pressing tools, such as w saws, reamers, files, gauges, die presses and drilling bits, that are usually made of steel, with a protective layer of chromium to render their surfaces relatively hard and nontarnishable.

Another object of my invention is to provide chromium-plated tools or implements that are tough, elastic and free from the buttleness which has heretofore been a characteristic of articles plated with chromium.

A still further object of my invention 1s to provide a process of producing chromiumcoated tools or implements that are nontarnishable and free from brittleness and that have a longer life and a better cutting or pressing surface than tools or implements made entirely of steel.

It has heretofore been the practice to make the tools or implements utilized for cutting or pressing operations from a high-grade steel. The life of such implements or tools, however, has been comparatively short, because of the extreme service to which they are subjected and this is true even when they are produced under the most favorable conditions, with respect to workmanship and the quality of material employed. Much difficulty has also been experienced with cutting tools made of steel, such as hack saws and files, because the grooves or interstices ca between the cutting edges have had the tendency to become clogged and this is especially true when they are employed for cutting or abrading soft surfaces. V

l have made the discovery that, when a tool or implement of any one of various kinds, such as files, hack-saw blades or drilling bits, gauges,'dies or presses, has been coated with a layer of chromium by my improved process, the hardness of the cutting 85 or pressing surface will be greatly increased,

npplicationfll ed necember 24, 1927. Serial No. 252,525.

and a non-tarnishable tool or implement that is superior in cutting or abrading properties will be produced.

It is well known that, when chromium is electro-deposited upon a metal, such as cop- 1 per, iron or steel, a surface is obtained that is considerably harder than the foundation metal upon which the chromium is plated. Attempts have been made to coat tools or implements that are subjected to severe usage, with chromium for the purpose of increasing their durability. Efforts alon this line, however, have not been successfu mainly because of the extreme brittleness that is imparted to the tools. By my -improved process, the elasticity of the foundation metal, which has been rendered brittle during the chromium-plating process, is restored, and chromium-plated tools or implements are produced that are freefrom britl0 tleness.

In practicing my invention, the tool or implement to be plated is first thoroughly cleaned of all dust and dirt by polishing with emery cloth of a very fine grade, or, if preferred, it may be cleaned by dipping in a dilute solution of sulphuric acid, an alkaline cleaning solution, or other pickling bath, and the excess pickling or cleaning solution may be subsequently removed by dipping in water.

The tool or implement, in its thoroughly cleaned condition, is then employed as a cathode in a chromium-plating bath, in conjunction with a lead or iron anode. Any of the well known chromium-plating baths may be utilized, but I prefer to use a bath composed of a dilute solution of commercial chromic trioxide. The commercial chromic trioxide usually contains sufficient chromic sulphate to afford a good plating solution, but, if necessary, additional amounts of either chromic sulphate or chemically pure chromic triox ide may be added to obtain the desired bath. The bath is preferably composed of the above specified ingredients in the proportions of about 33.3 ounces of chromium trioxide and one ounce of chromium sulphate to each gallon of water. While any suitable anode may be utilized, I prefer to place the solution thus obtained in a lead-lined wooden vessel, the lead lining serving as the anode and the tool or implement to be plated serving as the cathode.

When the temperature of such bath is kept at about 60 0., and a current density of two amperes per square inch is maintained at the cathode, a suflicient layer of chromium may be deposited upon the surface of the tools in about 30 minutes. It will be understood, however, that, at lower temperatures, a lower current density may be utilized, but it will require a longer time tode'posit' the layer of chromium upon the tool or implement.

Therefore, I do not desire to limit myself with respect to the constituents of the bath, the current density, or time required to plate the chromium u on the surface of the tool or implement, ut any bath may be utilized which,.at the requisite temperature and cur rent density, will produce the desired coating.

Tools or other implements provided with layers of chromium electro-deposited in the manner specified, are brittle and unsuitable for cutting or ressing operations. The exact cause of this rittleness is not known, but I believe that the hydrogen formed at the oathode during electrolysis is occluded into the foundation metal. After the implement or tool has been coated with a sufiicient layer of chromium, it is removed from the bath, suitably dried and subjected to a heat treatment to remove the occluded hydrogen. The temperature necessary to expel the hydrogen will,.of course, vary considerably but it should not be high enough to cause the layer of chr0- mium to alloy with the foundation metal or I to effect changes in the crystallization of the foundation metal which will decrease its hardness. When a chromium-platedtool is subjected to a temperature of from 50 to 350 C. for a period of from 1 to 24 hours, depending upon the size of the tool and the thickness of the chromium plating, the elasticity of the tool will be entirely restored.

The chromium-plated tools or implements obtained by my novel method are harder than steel, are non-tarnishable, and the toughness and elasticity of the steel or other foundation metal is not impaired in any manner. The life of tools plated. with chromium by my improved process is increased from two to fivefold; their hardness and cutting surfaces are superior to tools made of steel alone. and

. the interstices between the cutting teeth or blades made of steel. In a test made on drilling hits, it has been found that a bit made of the best grade steel would only drill 90 pieces of porcelain, but, when such bit was coated with chromium, by my improved process, it

was capable of drilling from 400 to 500 pieces.

The term tools as used in the specification and claim, is intended to include hack saws, drills, reamers, presses, gauges, dies and other implements-havmg pressing and abradmg as well as cutting surfaces.

' While I have described a specific form of my invention, it will be understood that various modifications may be made without departmg from the spirit and scope. of the invention. I desire, therefore, that only such limitations shall be placed on my invention as are imposed by the prior art and the appended claim.

- I claim as my invention:

The method of producing a chromiumplated tool which comprises electrodepositing a layer of chromium on a steel tool and then subjecting the chromium-coated tool to heat at a temperature of 150 to 350 C. for a period of from 1 to 24 hours, according to the size of the tool and the thickness of the chromium plating.

In testimony whereof, I have hereunto subscribed my name this 15th day of December,

BYRON V. MCBRIDE. 

